Merge pull request #61 from Farsx/master

Fixed hddtemp daemon detection
Merge pull request #62 from Farsx/master

Added hddtemp sensors in 'Show in panel' combobox setting

Closes #60
Closes #62
Removed duplicate async spawn code.
Added saveguard for calling hddtemp in preferences.
Return undefined instead of an empty array for detect* methods.
updated metadata for Gnome 3.8